Access vs. mobility: Happy people or happy cars?

When the federal transportation bill is renewed, many of the new transportation projects will be evaluated in terms of performance metrics for mobility and congestion, such as “hours of delay per 1000 vehicle miles traveled (VMT).” In other words, a “superior” design enables vehicles to travel many miles with few delays. Most of our highways are designed with this objective. This design metric suggests that the purpose of transportation/urban planning is to keep vehicles moving quickly and freely. The reason to do that is sometimes unclear — perhaps cars are happier when they’re moving?

If the purpose of transportation/urban planning is to serve humans, rather than cars, then other metrics are more appropriate.

The fundamental purpose of a transportation system is to provide people with comfortable access to what we want, in a short amount of time. Whether or not we use motorized vehicles to accomplish this access, is a secondary concern. In fact, energy independence would be best served if we used motorized vehicles as little as possible. Measuring convenient human access in terms of the speed of motorized light duty vehicles, is indirect and counterproductive. This is because transportation planners often minimize transportation choices in order to reduce delays per VMT — for example by shortening signal light durations, removing pedestrian crosswalks, and minimizing bike lanes. While increasing vehicular mobility, these measures reduce the safety and convenience enjoyed by pedestrians and cyclists. Some mobility metrics even ignore the load factor, i.e. the number of passengers carried in each vehicle.

Even if the load factor is included, mobility measures ignore the fact that many urban dwellers in mixed-use neighborhoods accomplish many of their errands by foot or bike, with zero VMT. Likewise, mobility measures ignore any difference between a 10-minute ride versus a 2-hour ride to accomplish the same errand, unless unplanned delays are involved. As an extreme example, imagine an urban street grid completely dominated by cyclists and pedestrians, with many nearby destinations, and a few vehicles wending their way through the crowd at 3 mph. Such an area would generate a poor “mobility” score, even though it serves many people with quick, convenient errands, while consuming minimal energy.

On the other hand, transportation choices can improve the mobility metric indirectly. If some potential drivers do not to use their cars, this leaves more room on the roads for the remaining drivers. However, this indirect tactic is rarely recognized in conventional transportation planning practice.

To measure timely human access more directly, metrics can track the hours consumed per errands completed. If all "errands" are too complicated to track, standardized lists can be used, such as kids to school and daycare, adults to work, weekly groceries, etc. If the human goals for the transportation system include energy savings, then metrics can include hours consumed per errands completed and energy used.

If the human goals for a transportation system also include human health and safety, community-building, minimal environmental impact, cost-effectiveness and delight, these goals can all be included in appropriate metrics. Transportation systems could easily be evaluated and designed in terms of all of these measures of human quality of life — for a tiny percentage of the cost of most vehicle-based “transportation improvement” projects. Since people pay for these systems, why settle for anything less?

If the fundamental goal of a transportation system is happy vehicles, then conventional vehicle-based metrics for mobility and congestion are appropriate. However, if the fundamental goal is happy people, then we need innovative performance metrics.

Levin Nock is a Sustainable Building Advisor, project manager, and research analyst. He was a founding board member of the Center for a Sustainable Today and ReCode Oregon. He has degrees in physics from Cornell University and engineering from Duke University and is certified as a Project Management Professional.